Biology Lab 8: Arthropoda

ecdysis in arthropods

periodically molting the hard exoskeleton and replacing it with a new, larger one, making growth possible

How was the ancestral condition (of segmentation and tagmatization) modified?

- Ancestral condition: similar segments, similar appendages (all legs) - Modern condition: higher degree of tagmatization with fusion of segments into regions and specialization of appendages (not all legs, some wings, maybe a stinger)

Eumetazoa

- Ex: Cnidaria - tissue level of organization, all animals except porifera

How do the clades nest together?

- Metazoa - Eumetazoa - Bilateria splits into protostomia and deurtostomia - Protostomia splits into spiralia and ecdysozoa

What are the four clades (subphyla) within Arthopoda?

- Myriapoda - Hexapoda - Crustacea - Chelicerata

What does vision look like with a compound eye?

- Often in movies, when vision is shown from an arthropod's compound eye perspective, it appears as multiple copies of the whole field of view. For example, seeing many flowers, when the arthropod was looking at only a single flower. - In reality, the compound eye produces an image of one pixelated flower, so it is slightly blurry

arthropod nervous system

- anterior brain - ventral nerve cord with segmental ganglia - arthropods have a variety of sophisticated sensory receptors sensitive to: mechanical stimuli, touch, vibration, water current, sound waves, taste, smell, light, gravity, humidity - the main idea is variety and sophistication

How do arthropods move with an exoskeleton?

- being encased in a hard external skeleton constrains body movement unless there is something in the body plan to relieve it - freedom of movement is provided by jointed appendages - there is movement possible at each joint, just as in our bodies - the limbs are paired, as you might expect for a bilaterally symmetrical organism

How is growth possible in Arthropods when they have a cuticle as their exoskeleton?

- being encased in a non-living hard skeleton could place a constraint on growth - this constraint is relieved by the process of ecdysis

tracheae

- branching tubes - after air enters the body, it travels through the tracheae - the tracheae branch into smaller tubes called tracheoles

Which of the subphylas have mandibles?

- crustacea - hexapoda - myriapoda (cehlicerates do not have mandibles)

Subphylum Crustacea - representative - tagmata (specific names) - appendages and uses of them (specific name of one)

- crustacea have 3 tagmata: head, thorax, and abdomen - in some species, like the crayfish, the head and thorax are fused together to form a cephalothorax which is covered by a single large shield called the carapace - the cephalothorax has legs which may be specialized for use in walking or feeding - the crayfish has five pairs of walking legs - the first pair is modified into a large claw called a cheliped - the abdomen has appendages usually used for swimming, water circulation over gills, and in females that carry fertilized eggs

What are the four arthropoda subphyla and the model organisms?

- crustacea: crayfish - myriapoda: centipede - hexapoda: grasshopper - chelicerata: garden spider and friends

What three ways is the success of Arthropods defined?

- diversity - abundance - distribution

Subpyhlum Chelicerata (continued) - eyes - appendages (two pairs)

- eyes are ocelli - 1st pair of appendages: chelicerae = in spiders there is a fang at the tip that injects venom into prey - 2nd pair of appendages: pedipalps = sensory, feeling, food manipulation, copulation

Gills in Aquatic Crustaceans

- gas exchange occurs between the water and the blood in the gills, just as in the molluscs - a cross section of crayfish body shows that gills are protected by the exoskeleton, but water can enter it on the ventral side - the gils have a feathery appearance (lots of surface area - gills are filled with blood and do gas exchange

How is the exoskeleton a key to success?

- hard enough for protection - light enough for mobility - versatile thickness and flexibility (exoskeleton is thin and flexible at joints, but thick, hard, and rigid over other parts such as claws)

Crustacaea tagmata

- head, thorax, abdomen - some have cephalothorax and abdomen

What are horseshoe crabs?

- horseshoe crabs are not really crabs - they belong to the group of arthropods called Chelicerata

Do arthropods have a hydrostatic skeleton?

- in arthropods a hydrostatic skeleton is not possible with an exoskeleton - one of the requirements of a hydrostatic skeleton is a flexible body wall which is not true of the hard exoskeleton

What is a downfall of ecdysis in arthropods?

- individuals are vulnerable after molting and before the new exoskeleton hardens - it has been reported that approximately 85% of arthropod deaths occur during molting - this includes potentially difficult molts late in life, when the individual has become relatively large

Cnidaria

- jellyfish, anemones, coral - radial symmetry - diploblastic

Subphylum Myriapoda - representative, what it means - tagmataization - habitat - modified appendages - feeding strategy - body shape

- many feet, centipede is representative - low level of tagmatization, 2 tagmata, head and trunk - terrestrial, but do not have well-developed waxy layer in exoskeleton so needs to be in moist environment - 1st trunk appendages modified into poison claws that stab prey and inject poison strong enough to subdue small vertebrates - goes with feeding strategy as predator - rest of trunk appendages have some morphology (form) - centipede has one pair of walking legs on each segment; project to side of body = designed for speed - flattened body shape

A specialized gas exchange surface must have these characteristics: (4)

- moist surface and must be protected from desiccation - thin and permeable to gases - lots of surface area - vascularized

What two things provide movement then?

- muscles - jointed appendages

How are muscles arranged/organized in arthropods? How is this different from our muscle system?

- muscles are arranged as localized bands of muscles and are organized into antagonists at joints such as flexors and extensors - one group contracts and bends the joint one way, then it relaxes and the other contracts and bends it the other way - this is similar to the arrangement of our own muscles except in arthropods the muscles are attached to the inside of the skeleton

Ecdysozoa - what organisms are included

- nematoda: round worms, blastocoelomates - Anthropoda: myriapoda, chelicerata, hexapoda, crustacea, reduced coelom, Hemoceol is main body cavity

Where do crustaceans live and why?

- no well developed waxy layer in exoskeleton - terrestrial crustaceans are confined to moist habitat - need to live in water or in a moist environment

Spiralia - what organisms are included? - body cavities?

- platyhelminthes: free living planaria, tapeworms, flukes, aceolomate - Annelida: segmented worms, coelomate - Mollusca: polyplacaphora, Gastropoda, Bivalvia, Cephalopods, reduced coelom, homoeceol is main body cavity

Chelicerata tagmata

- prosoma (cephalothorax) and opisthosoma (abdomen) - head is reduced

Subphylum Chelicerata - representative - tagmata - outer body covering? - mandibles? - antennae?

- representative is garden spider and "friends" - 2 tagmata: prosoma (fused head and thorax) and opisthoma (abdomen) - waxy cuticle - no mandibles - no antennae (in fact, chelicerates don't appear to have a defined head, when you look at the diagram to the right it appears that the head is missing compared to a hexapod

What would the ventral view of crayfish show?

- shows cheliped and walking legs on thorax - crustacea have appendages on abdomen - some, like crayfish, use them to hold fertilized eggs

centipede antenna

- since eyes do not form images, antenna play important sensory role - they are highly sensitive and contain many touch and chemical receptors

Subphylum Hexapoda - meaning, representative - tagmata - habitat and why - appendages and location - mandible? - kind of eyes - type of gas exchange (how does this help them with their habitat)

- six footed, grasshopper - 3 tagmata: head, thorax, abdomen - waxy exoskeleton so it isn't restricted to a moist habitat - 3 pairs of walking legs on thorax, wings on thorax - no appendages on abdomen - hexapods have mandibles - ocelli and compound eyes - tracheal system - spiracles on abdomen - able to close spiracle which decreases desiccation - they are found in all habitats on land and in fresh water - there are very few marine hexapods

spiracles

- small openings on the body - where air enters the body - can be closed to prevent desiccation

The exoskeleton provides: (5)

- structural support - attachment for muscles for locomotion - protecting against predators of the same scale - prevention of water loss (desiccation) - an integral part of sensory receptors

What are the two ways tagmata can be connected in chelicerata?

- tagmata can be braodly fused - tagmata can be joined by slender pedicel

Cuticle of Arthropods - what is it? - why is it important? - is it living? - what layer secretes it?

- the cuticle forms an exoskeleton in arthropods - an exoskeleton supports the body from the outside - the segments and limbs of arthropods are encased in this hard external skeleton - the cuticle is to a large extent responsible for the success of this phylum - the cuticle is on the outside of the body and is secreted by the epidermis - it is non-living

Layers of Cuticle - how do the layers differ based on habitat? - what function do the layers serve?

- the outer layer of the cuticle is a thin waxy layer (in arthropods well-adapted to terrestrial habitats, this layer is well-developed) - the waxy layer is a barrier against evaporation of water from the body and hence prevents desiccation, an important consideration for terrestrial animals - the inner hardened layer is composed of chitin and reinforced by the addition of minerals and/or proteins - the thickness and flexibility of this layer varies in different parts of the body and in different arthropods - epidermis is inner layer that secretes the other layers that form the cuticle

Tracheoles

- the smaller tubes - air travels through these tubes to the surface of the cells

What gas exchange strategy do crustaceans use?

- they use gills for gas exchange - the gills are underneath the carapace and are attached to walking legs

What are the basic steps for the closed circulatory system?

-A dorsal heart to pump the blood into arteries. Valves prevent blood from flowing back into the heart. -The arteries deliver blood to the hemocoel. -The blood drains back to the space surrounding the heart. The hemocoel in arthropods is much more extensive than in molluscs. -The blood returns and enters the heart through openings on the heart called ostia. (for some arthropods, the blood distributes nutrients to the cells of the body and in some arthropods it also distributes gases)

Tagmatization - what are the two aspects? - what is the name of the functional groups?

1.) fusion 2.) specialization - During development, segments fuse to form functional groups called tagmata (tagma = singlualr) - Specialization of appendages is associated with different tagmata

What is cool about arthropods evolutionary history of habitats?

After the first arthropods made a success of aquatic habitats, members of the phylum eventually became, not only the first animals to make the land their home, but also the only invertebrates to fly and to successfully adapt on a large scale to life on land

Arthropodization

Anthropods have a suite of adaptive characteristics that evolved that complement one another and produce a highly successful body plan

Adaptations for Terrestrial Life: Here are the challenges to terrestrial life and the arthropod solutions

Challenges: 1.) dessication, loss of water across the body surface 2.) gas exchange surfaces exposed to air will dry out 3.) support on land without the aid of buoyancy of water 4.) loss of water with excretions of nitrogenous waste 5.) many aquatic animal release gametes into their watery environment and fertilization occurs in the water. However, if terrestrial animals did this, the gametes were dry out and perish Soultions: 1.) well developed waxy layer in cuticle (Hexapoda, Chelicerata) 2.) Gas exchange strategies that place gas exchange surface internally: book lungs (chelicerata), tracheal system (Hexapoda and myriapoda), spiracles that close (hexapoda) 3.) hard exoskeleton supports weight of body on land 4.) nitrogenous waste in form of solid, uric acid 5.) fertilization occurs internally with male placing sperm inside female

Review Slide of 4 Gas Exchange Strategies

Aquatic Arthropods: Gills and Book Gills use the same overall strategy (which is the same strategy as the gills of a mollusc) -Both have lots of surface area and are exposed to surrounding water. -Water passes over gills/book gills. Gas exchange occurs between surrounding water and blood: oxygen into blood and carbon dioxide into water -Blood then transports gases from gills to rest of body where gas exchange occurs between blood and cells: oxygen to cells and carbon dioxide into blood, blood returns to gills Terrestrial Chelicerates: Book Lungs Gas exchange surface is located internally - Book lungs are layers of thin, page-like structures filled with blood. They are located in an air-filled space in the body. -Air enters through slits in body wall and passes over moist surface of vascularized book lungs. -Gas exchange occurs between air and and blood in book lungs: oxygen into blood and carbon dioxide into the air -Blood then transports gases from book lungs to rest of body where gas exchange occurs between blood and cells: oxygen to cells and carbon dioxide into blood, blood returns to book lung Tracheal System: Hexapoda and Myriapoda This is another gas exchange strategy adapted to terrestrial life so the gas exchange surface is located internally - Air enters through openings in body wall called spiracles. It then travels through a series of branching tubes. Eventually, tubes branch near enough to each individual cell for efficient diffusion of gases to occur -Gas exchange occurs between air in the tubes and individual cells: oxygen into cells and carbon dioxide into tubes, air travels back to outside of body through same tubes

Excretion of nitrogenous waste in aquatic arthropods - what is the form?

Aquatic arthropods excrete nitrogenous waste in form of ammonia. Ammonia is toxic and must be eliminated quickly. It is soluble in water so aquatic arthropods can excrete it in the water around them and it will be carried away. Notice in the diagram on right that the chemical structure for ammonia is similar to the amino group from the protein. This means it does not require a lot of energy to convert amino acids into ammonia

Segmentation

Arthropods have segmented bodies: series of repeated units

Molting & Size

Arthropods shed their rigid exoskeleton and go through a "squishy" stage until new exoskeleton hardens. The laws of physics make it clear that a large terrestrial animal with no means of protection or body support will deform and have a difficult time moving. Natural selection would probably act against a large animal that faced so many extra challenges when molting.

What are two strategies that are adaptations to terrestrial life for gas exchange? Are they similar or different?

Book Lungs and Tracheal System - they do gas exchange in different ways

How does the exoskeleton impact size? - what are the two reasons?

Features of exoskeleton result in constraint of size (they are relatively small animals) Reasons: - molting - exoskeleton weight and strength

What are the two strategies used by aquatic arthropods for gas exchange? Are they similar or different?

Gills and Book Gills - very similar in how they do gas exchange

Exoskeleton weight and strength & Size

If you scaled up an ant 4X proportionally (keeping its exoskeleton thickness the same in relation to its body), the ant's legs would crumple under the strain of holding up its body.

Abundance of Arthropods

It is estimated that there are 10^18, or a billion billion, arthropods on Earth; Anthropods constitute 84% of all known animal species

Reminder of Functions of Cuticle as an Exoskeleton

Protective barrier, keeps some things in and others out: •prevents loss of water (desiccation) from body •prevents pathogens and parasites from entering -Protection from predation and physical injury -Responsible for structure, support and form -Movement •Rigid skeleton for muscle attachment •Soft and flexible at hinge- like at joints -Sensing •The cuticle is non-living, so the cuticle itself cannot provide sensory information. However, the cuticle is modified so that sensory nerve endings are lodged in parts of the cuticle modified into bristles, peglike projections, cones, pits, or slits in the cuticle. These sensory receptors are specialized to sense chemical, temperature, touch, gravity, and humidity sensations.

What clade do most animals belong to?

Protostomia

What kinds of eyes can arthropods have?

Some arthropods have only ocelli eyes, some only compound eyes, and some have both.

Excretion of nitrogenous waste in terrestrial arthropods - what is the form?

Terrestrial arthropods excrete nitrogenous waste in form of uric acid. These arthropods need to conserve water. Uric acid is non-toxic, insoluble in water, precipitates as a solid with little loss of water to eliminate it from body. This is an important adaptation to terrestrial life. Also notice in the diagram to the right how much more complex the chemical structure for uric acid is compared to the amino group. It requires more energy to make, but the conservation of water is worth it.

What is the difference between book gills and book lungs? How does this explain the horseshoe crabs gills?

The difference between book gills and book lungs is that the book lungs have to be protected from desiccation since spiders are terrestrial and so are placed inside the body. Horseshoe crabs are aquatic and do not need to protect the book gills from desiccation since they live in water.

What are the parts of the digestive tract and what do they do?

The digestive tract is generally typical and really not that different from our own •Foregut (mouth, esophagus, stomach) where ingestion, transport, storage, and mechanical digestion occur •Midgut (digestive gland, intestine) where chemical digestion and absorption occur •Hindgut (rectum, anus) where water absorption occurs and feces are prepared and then eliminated

Diversity of subphylum crustacea

The diversity of body forms and lifestyles of crustaceans is enormous. There are crustaceans in every type of marine and freshwater environment, and terrestrial forms. Members of Crustacea display a very high degree of variation in the tagmata and the appendages. They are so diverse that it is difficult to use one crustacean as a representative. For learning purposes, we are going to use the crayfish as the representative.

What do mandibles do?

The mandible are a mouthpart used for chewing (biting, cutting). It is similar to our mandible (lower jaw), but the arthropods use their pair of mandibles in sideways motion instead of up and down.

Tracheal system

The tracheal system is a gas exchange adaptation for terrestrial life in insects and centipedes and millipedes. The gas exchange surface is the individual cells of the body which are internal, so there is no risk of desiccation. It is a series of branching tubes extending from opening in body wall that carry air to and and from each individual cell. When the air reaches the cells, gas exchange occurs between the air in the tube and the moist surface of the cell.

Why do spiders use book lungs? How would you describe a book lung?

They can't have their gas exchange structure suspended in air or they would dry out and not be able to do diffusion. Their gas exchange structure has to be internal. Imagine a modified book gill of the horseshoe crab with all its layers, placed inside a chamber in the body that remains humid. Then imagine a small opening on the ventral side of a spider that allows air to come in and out, but not enough to dry the surface out. The layers of blood-filled "pages" in the chamber could then exchange gases with the air.

What can be used to identify a crustacean?

a characteristic that you can always look to identify a crustacean is 2 pairs of antennae - helpful because there is a high degree of specialization of the appendages for a variety of functions

Diversity of Arthropods

a million species identified and many, many yet to be recognized (compare this to 60,000 vertebrate species)

internal fertilization

adaptation for terrestral life

excretion of uric acid

adaptation for terrestrial life

variety of gas exchange structures

adaptation to terrestrial life

versatile exoskeleton

adaptation to terrestrial life

flight

adaptive for moving/escaping

Metazoa

all animals - eukaryotic - multicellular - heterotrophic - ingest food - Ex: Porifera

What are the vast majority of animals within protostomia?

arthropods - they have radiated to occupy every conceivable type of ecological niche

Bilateria

bilateral symmetry, triploblastic

What type of digestive tract do arthropods have?

complete digestive tract with regional specialization

Deuterostomia

blastopore forms anus

Protostomia

blastopore forms mouth

What plays no part in the gas exchange of the tracheal system?

blood

What kind of gills does the horseshoe crab have?

book gills

Where are the book gills located?

book gills are located on the ventral side of the horseshoe crab

What kind of gas exchange do chelicerates use?

book lungs - recall that horseshoe crabs are chelicerates and they have book gills -

What kind of gas exchange structure do spiders use?

book lungs (chelicerata subphylum)

small size

exploit many more niches compared to larger animals

What type of body cavity do arthropods have?

coelomate - Arthropods are coelomates, but the coelom is reduced to the space surrounding the heart

What kind of eyes do crustaceans have? Do they have antennae?

compound eyes - often times, as in crayfish, they are on stalks - 2 pairs of antennae

complete metamorphosis (86% of insects)

different stages of life use different parts of habitat reducing competition

What are the reasons the centipede is confined to moist habitats even though it is terrestrial?

due to lack of waxy layer in cuticle and open spiracles - for most species, the spiracles remain open at all times which is another reason they must live in moist habitats - air can enter the spiracles and cause desiccation

complex behavior

evolution of social systems

The ___ is a defining feature of arthropods and key to their success.

exoskeleton

Mandibles

functions as jaws, sideways compared to ours

cephalothorax

fusion of head and thorax

Where does gas exchange occur in this tracheal system?

gas exchange occurs between the air in the tubes and the individual cells

Myriapoda tagmata

head and trunk

Hexapoda tagmata

head, thorax, and abdomen

What is the main body cavity in arthropods?

hemocoel - composed of connected spaces around tissues and organs

What subphyla use the tracheal system?

hexapoda and myriapoda

compound eye

image forming, many separate units each with lens

What is another defining characteristic of arthropods? - arthro = - pod =

jointed appendages - joint - leg

produce many offspring in a lifetime and offspring mature rapidly

large amount of genetic diversity

Why does the abdomen pulse in insects?

larger and more active insects, such as moths, butterflies, bees and wasps, show breathing movements - that is they actively pump air through the tracheal system

segmentation + tagmatization

makes possible many variations of mouthparts, walking legs, etc. which allows arthropods to explore wide range of ecological niches

Centipede eye type

ocelli - can be just a few, or a cluster of ocelli, which makes it look like a compound eye - as ocelli, they are not image forming - only light and dark

What type of circulatory system do arthropods have?

open circulatory system

cephalothorax with carapace - what is carapace?

shield like exoskeleton plate that covers the cephalothorax in some

ocelli eyes

single lens, simple cup that is light sensitive, generally non-image forming - image of a hexapod with both ocelli and compound eyes

Porifera

sponges - cell level of organization - multicellular - placed in metazoa

Tagmata

tagma is a specialized grouping of multiple segments into a coherently functional morphological unit

What kind of animal are spiders?

terrestrial arthropods

Anthropod success

there are many reasons for their success, which are listed in the following notecards

What are the book gills covered by?

they are covered with flaps of exoskeleton, so you can lift the flap and see layers of the gills, like pages in a book

Distribution of Arthropods

they live in every type of environmental habitat - sea, freshwater, on land, and in the air

What gas exchange strategy do centipedes use?

tracheal system

___ ___ forms the exoskeleton.

versatile cuticle